The present invention relates to a printing head, a printing apparatus which employs a printing head, and a printing method which employs a printing head.
In the past, a printing apparatus for printing an image on printing medium such as paper, fabric, plastic sheet, and OHP sheet (hereinafter, simply xe2x80x9crecording paperxe2x80x9d) has been embodied in the form of an apparatus in which one of various printing heads based on the wire dot system, thermal system, thermal transfer system, or ink jet system can be mounted.
The ink Jet printing system prints an image on a sheet of recording paper by ejecting ink from ink ejection orifices. In other words, it is not an impact type printing system, and therefore, the printing noise it produces is substantially low. Thus, a printing apparatus based on the ink jet printing system (hereinafter, xe2x80x9cink jet printing apparatusxe2x80x9d) can print a high density image at a high speed.
In recent years, demand has been rapidly increasing for higher speed and precision, and therefore, it has become common that an ink jet printing head is provided with a large number of ink ejection nozzles, the orifices of which are arranged as illustrated in FIG. 1. As for the ink ejecting systems for an ink jet printing head, there are those which use thermal energy, and those which use mechanical energy. In the case of the former, a heat generating member (heater) such as an electrothermal transducer is driven to generate heat which generates bubbles in ink, and the bubbles eject ink. In the case of the latter, a piezoelectric element is employed as an ejection energy generating element (recording element), and the contraction of the element which occurs as the element is driven is used to eject ink.
Both the printing head which employs the former, and the printing head which employs the latter, suffer from certain problems. That is, if a printing head is designed so that all the elements are driven at the same time, cross talk or the like occurs, which changes the amount of ink per ejection, reducing print quality. Further, in order to drive all the elements at the same time, a power source with a capacity large enough to instantly flow a large amount of electrical current is required. There are solutions to these problems. According to one of the solutions, for example, the large number of ink ejection nozzles (which comprises an ink ejection orifice, a liquid flow path, an ejection energy generating element, and the like) are divided into a plurality of blocks, each of which comprises a predetermined number of ejection nozzles. In operation, each ejection nozzle in each block, being correspondent to an ejection nozzle orifice in the rest of the blocks, in terms of the ordinal position in its own block, is caused to eject ink at the same time as the ordinally correspondent ejection nozzles in the other blocks. Further, the ejection nozzles in the same block are caused to sequentially eject ink.
More specifically, referring to FIG. 1, (A), a printing head 1 is provided with a large number of ink ejection nozzles 2, which are divided into blocks, each of which comprises 16 nozzles. In operation, ordinally correspondent nozzles in all blocks (for example, the first, seventeenth, thirty-third, and so on, in terms of the order inclusive of all the nozzles), are driven at the same time, and the nozzles in each block are sequentially driven. In other words, every sixteenth nozzle, is driven at the same time, and therefore, the ink ejection of each nozzle is not affected by the ink ejection by the adjacent nozzles, that is, cross talk is minimized
However, if printing is done by using the above described block based sequential driving method while moving a printing head, the ejection orifices of which are aligned in the direction parallel to the secondary scanning direction (direction in which printing head and printing medium are moved relative to each other), in the primary scanning direction different from the direction in which the ejection orifices are aligned, the dots formed by the ink ejection from 16 nozzles in each block align at an angle, as illustrated in FIG. 1, (A).
This problem has been dealt with by aligning the orifices of the ink ejection nozzles at an angle proportional to the degree of the staggering of the time at which each nozzle in each block is driven, in other words, by mounting the printing head at an angle relative to the secondary scanning direction, so that the direction in which the dots formed by the staggered ink ejection align, becomes parallel to the secondary scanning direction. However, if this method is used, it is difficult to realize two or more degrees of resolution in terms of the primary scanning direction, by controlling the angle at which the orifices of the ink ejection nozzles are aligned, and/or by controlling the length of the intervals between the adjacent points in time at which the nozzles in each block are sequentially driven Thus, in the case of a printing apparatus which uses this method, it is common that only the pitch at which a printing head is moved in the secondary scanning direction can be adjusted, and therefore, resolution can be adjusted in terms of only the direction parallel to the secondary scanning direction.
Obviously, image quality is further improved if resolution is increased in the primary scanning direction as well as the secondary scanning direction. However, when the frequency at which a printing element such as the electrothermal transducer or piezoelectric element is fixed, the scanning speed of a printing head in the primary direction must be reduced in order to increase resolution, and therefore, the throughput of the printing apparatus reduces.
Some printed images require a high degree of resolution, for example, images used in medical fields, and some images are required to be printed at a high speed instead of being printed at a high degree of resolution. In other words, the requirement in terms of resolution varies depending on the usage of the printed images.
Thus, the primary object of the present invention is to provide a printing apparatus which is simple in structure and yet is capable of satisfying users in terms of resolution, throughput, and the like.
A printing head in accordance with the present invention which accomplishes the above described object is characterized in that it comprises a plurality of printing nozzles for adhering printing agent to printing medium, can be driven at various speeds so that various degrees of resolution can be realized, and moves relative to the printing medium as it adheres the printing agent to the printing medium, and also that it comprises a timing adjusting means for adjusting the timing with which the printing elements are driven in response to the selected resolution so that the physical intervals between the two adjacent dots in terms of the direction in which the printing head scans the printing medium can be controlled.
Further, the printing apparatus is provided with a driving means which divides the plurality of printing nozzles into a plurality of blocks which comprises a predetermined number of printing nozzles, and is capable of driving the plurality of blocks in continuous sequence, as well as driving the printing elements in each block at the same time, and the aforementioned driving timing adjusting means is enabled to adjust the printing element driving timing by adjusting the number of the blocks into which the plurality of the printing nozzles are divided by the driving means.
Further, the printing apparatus may be provided with a means for adjusting the amount by which the printing agent is adhered, per ejection, to the printing medium by the plurality of printing elements, in response to the adjustment in the driving timing.
More specifically, each of the plurality of printing nozzles is provided with a plurality of means for generating energy for adhering the printing agent to the printing medium, and the amount by which the printing agent is adhered to the printing medium is adjusted by selectively driving the plurality of these energy generating means by the aforementioned means for adjusting the ink amount.
Further, the printing apparatus in accordance with the present invention may be provided with an additional means which is capable of carrying out the above described plurality of printing operations different in the driving timing for the printing elements, and/or one or more of other printing operations, and also is capable of carrying out one or more printing operations externally selected from among the above described printing operations, in response to an external signal which specifies at least one of the above described printing operations.
The signal which specifies the printing operation may be enabled to double as a signal which changes resolution by changing the aforementioned driving timing for the printing elements.
The printing apparatus may be provided with means other than the means for changing the driving timing for the printing elements, for example, a means for reading an image.
The means for receiving the external signal which specifies the printing operations may be such a signal receiving means that can double as a signal outputting means.
The aforementioned printing nozzles are provided with ejection orifices through which ink as the printing agent is ejected to be adhered to the printing medium, and a means for generating the energy to be used for ejecting the ink. The printing head is constituted of an ink jet printing head.
The means for generating the energy to be used for ejecting the ink may be provided with one or more electrothermal transducers which generates thermal energy as electrical current flows through them. In this case, the ink is ejected from the ejection orifice with the use of the so-called film boiling caused in the ink by the thermal energy applied to the ink by the electrothermal transducer.
The printing apparatus in accordance with the present invention is characterized in that it comprises a printing head mounting means for mounting any of the aforementioned printing heads into the main assembly of the printing apparatus, and a means for moving, relative to the printing medium, the printing head mounting means in the direction different from the direction in which the orifices of the plurality of printing nozzles are aligned.
Further, the printing apparatus may be provided with a means for providing the printing head with signals which change the driving timing for the printing elements.
The printing system in accordance with the present invention is characterized in that it comprises a means for supplying an image forming apparatus in accordance with the present invention with image formation data, and a means for setting the degree of resolution at which the image formation data are embodied in the form of a printed image.
The printing method in accordance with the present invention is characterized in that it moves, relative to the printing medium, any of the aforementioned printing heads in the primary scanning direction different from the direction in which the orifices of the plurality of printing nozzles are aligned, and changes the timing, with which the plurality of printing elements are driven, in response to the resolution set by an operator.
The printing apparatus in accordance with the present invention is characterized in that it comprises a means for moving, relative to the printing medium, the printing head which has a plurality of printing elements for adhering the printing agent to the printing medium, and a driving timing changing means for changing the intervals, in terms of the moving direction of the printing head, between the adjacent two dots to be formed, in accordance with the selected resolution, by changing the driving timing for the printing elements.
The printing method in accordance with the present invention is characterized in that it employs the printing head, which has a plurality of printing nozzles for adhering the printing agent to the printing medium, can be driven in accordance with different degrees of resolution, and prints an image while being moved relative to the printing medium, and also that it can change the intervals, in terms of the moving direction of the printing head, in accordance with the selected resolution, by changing the driving timing for the printing elements in accordance with the selected resolution
In this specification, xe2x80x9cprintingxe2x80x9d or xe2x80x9crecordingxe2x80x9d means not only forming (printing) patterns with a specific meaning, for example, letters or the like, but also general patterns with no specific meaning, on a piece of printing medium. The xe2x80x9cprinting mediumxe2x80x9d means not only such paper that is generally used with a recording apparatus, but also fabric, plastic film, metallic plate, and the like, in other words, any such medium that can take printing agent, for example, ink, processing solution, or the like, ejectable from the printing head.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.